Asian countries where herbal treatments are rooted had the most incidence.

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Naturopaths and other gurus of “alternative medicine” love to tout the benefits of traditional herbal medicines. For instance, Aviva Romm—a Yale-educated doctor who publicly defended Gwyneth Paltrow’s lifestyle site Goop then later called it a “caricature of everything alternative health for women”—sells her own line of unproven herbal remedies. Billionaire Susan Samueli—who donated $200 million dollars alongside her husband so the University of California, Irvine, could open an “integrative” medicine program—promotes homeopathy, naturopathy, and runs an active consulting practice versed in Chinese herbs.

Herbal remedies are often seen as harmless, soothing treatments that tap into the ancient wisdom of traditional healing. While that may be the case for some, there are also those that cause cancer—and sometimes it’s nearly impossible to tell one from the other.

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According to a study published Wednesday in Science Translational Medicine, traditional components of herbal remedies used throughout Asia are widely implicated in liver cancers there. In Taiwan, for instance, 78 percent of 98 liver tumors sampled displayed a pattern of mutations consistent with exposure to herbs containing aristolochic acids (AAs). These are carcinogenic components found in a variety of centuries-old herbal remedies said to treat everything from snakebites to gout, asthma, and pain.

Because of their toxicity, some (but not all) of the herbs and plants known to contain AAs have been banned in Taiwan and other places. These flora tend to come from the genera Aristolochia (e.g., birthwort, pipevine) and Asarum (wild gingers). The Food and Drug Administration has also issued several warnings and advisories over AA-containing remedies.

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Still, they remain easy to buy online. And many AA-containing herbs may be hidden in traditional formulations, mislabeled, or not clearly labeled. Studies done on products found to contain AAs show that their levels are extremely variable and can sometimes be very high.

“Our findings reinforce the idea that the use of natural herbal medicine may not be without risk,” the Belgian doctors concluded. They also noted that similar cases had been reported in France, Spain, Japan, the United Kingdom, and Taiwan.

Harmful herbs

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AAs spur cancers almost exclusively by inducing adenine-to-thymine (A-to-T) mutations in DNA. When such mutations strike in genes that are known to be able to drive cancers, a tumor can develop. In the new study led by computational biology and cancer researcher Steven G. Rozen of the Duke-NUS Medical School in Singapore, researchers found AA-associated mutations in a variety of these types of genes. They also found that some mutations deactivated other genes, which may promote cancer by “diverting energy into cancer-relevant metabolic pathways.”

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To get a sense of how widespread AA-associated cancers may be, Rozen and his colleagues collected tumor tissue samples from patients with liver cancers. The samples were not selected based on suspicion of the patient taking herbal remedies; they were simply convenience samples. Next, the researchers sequenced the DNA from the cancer cells and compared them with matched, healthy liver tissue. With the sets of genetic codes, the researchers looked for patterns of AA-associated mutations. These patterns were largely based on previous research into AA-induced mutation signatures.

Maps showing prevalence of aristolochic acid-related cancers around the world.

The researchers found that 76 of 98 liver tumor samples (78 percent) from Taiwan had signs of AA-exposure. Of the 89 from China, 42 (47 percent) showed signs of AA-induced mutations. Of 231 samples from South Korea, 29 (13 percent) showed signs of AA-exposure. The percentages were much smaller for samples taken from Japan, Europe, and North America—ranging from just one to nearly five percent. However, 21 percent of 89 liver-cancer samples from Asian patients at the Mayo Clinic in the US also showed signs of AA-exposure.

In light of the data, Rozen and his colleagues say it’s necessary to educate patients and the public about the risks of AA-containing herbal remedies. However, they note, that might not be enough:

In addition, the traditional nomenclature is confusing, making it difficult for consumers and suppliers to be sure of plant identification or of the constituents of multi-herb preparations; there is ample evidence that mislabeling is common.